Main emphasis during the following year will be given to natural differences of the arterial wall in two strains of pigeons: Show Racer (atherosclerosis resistant) and White Carneau (with spontaneous atherosclerosis). After we determined that the Show Racers aortae have a significantly higher activity of the sympathetic nerve endings than aortae from White Carneau, we propose a detailed quantitative histology and histochemistry of the media to further clarify the differences in the metabolic behavior of blood vessel walls of both strains of pigeons. Mechanical properties of arteries vary with the anatomical location. This finding will be further analyzed in a series of experiments where partial or complete digestion of collagen (collagenase) or elastin (elastase) will be induced. The amount of connective tissue digested will be established biochemically and the mechanical properties will be determined experimentally. These experiments represent the ground work for a better understanding of the structural vessel wall changes induced by sympathectomy.